Such filter media are employed for the filtration of industrial fluid streams, for example, in hot-gas applications such as waste incineration plants, cement kilns and coal furnaces. The filter medium according to the invention can be used, for instance, in so-called bag-filter systems in which the filtering bags made of the filter medium are pulled over support cages. Over the course of time, the textile filter material has to be cleaned and the dust cake that has deposited on the filters has to be removed.
A very efficient cleaning method is the so-called “pulse-jet” method in which pulses of compressed air cause the textile filter material to move, as a result of which the dust cake can be cleaned off the filter. Due to the cleaning procedure, the filter media are subjected to high levels of mechanical stress, which entails the risk that the staple fibers might unravel from the fabric and/or that the fabric might become damaged.
Before this backdrop, European patent application EP 0 962 243 A2 discloses a filter medium of the type mentioned above that is characterized, among other things, by high dimensional stability as well as temperature and chemical resistance. In spite of a sparse covering with staple fibers, crosswise breaks in the fabric after such a pressure step are essentially ruled out since it is practically impossible for unraveling to occur, as a result of which the value does not fall below the requisite minimum number of crosswise staple fibers needed to prevent crosswise breaks.
For purposes of improving the mechanical stability of filter media, European patent application EP 1 391 660 A1 discloses filter laminates that have a membrane made of expanded porous polytetrafluoroethylene, a support fabric likewise made of polytetrafluoroethylene as well as staple fibers—also made of polytetrafluoroethylene—that are needled onto the support fabric. The staple fibers are joined to the membrane by means of a fluorinated polymer that serves as an adhesive.
Finally, European patent application EP 1 862 208 A1 discloses a filter medium having a support fabric containing basalt fibers, whereby at least one side of the support fabric is provided with polymeric staple fibers.